Grease has been so far applied to gears or sliding parts as a lubricant. Nowadays, plastic members have been more and more incorporated into automobile parts, home electrical appliances, OA devices, etc. as gears or sliding parts to attain requirements for lighter weight, lower cost, etc. The conventional grease so far used to lubricating parts of metallic members, when if applied to lubricating parts of plastic members, cannot satisfactory in respect to lower the friction coefficient or improve the durability.
A grease composition for plastic members, which comprises fine particles of polytetrafluoroethylene having an average primary particle sizes of less than 0.2 μm has been so far proposed as a grease composition having a distinguished wear resistance, capable of reducing wear of plastic members, when used under severe conditions, but still has a durability problem, even though the wear of plastic members can be suppressed by the proposed grease composition.    Patent Document 1: JP-A-2001-89778
Among the sliding parts, power transmission system parts, particularly those used in automobiles, etc. have more and more incorporated plastic members. For example, a combination of a metallic worm gears with a plastic worm wheel gears has been more and more used in the moderation mechanism. For a grease composition for lubrication of the metallic member and the plastic member as the sliding members of the power transmission system, a lubricating grease composition, which comprises, for example, a larger amount of fluororesin powders and a smaller amount of a thickening agent, has been so far proposed, but also still has a durability problem, even though the friction coefficient can be lowered in a wide temperature range by the proposed composition.    Patent Document 2: JP-A-2002-363589